Acids and Bases Equations
Complete equation reference for IGCSE Chemistry 0620 acids and bases: neutralisation, acid reactions with metals, carbonates, and oxides.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
This page collects every acid-base equation pattern required for 0620, with conditions, observations, and salt-prediction rules. Use it alongside acid-base theory and preparation of salts.
Predicting the salt
| Acid | Anion | Salts formed |
|---|---|---|
| Hydrochloric acid (HCl) | Cl- | Chlorides |
| Sulfuric acid (H2SO4) | SO4^2- | Sulfates |
| Nitric acid (HNO3) | NO3- | Nitrates |
The cation comes from the metal, oxide, hydroxide, or carbonate.
Pattern 1: Acid + Metal -> Salt + Hydrogen
Applies to metals above hydrogen in the reactivity series.
| Equation | Observations |
|---|---|
| Mg + 2HCl -> MgCl2 + H2 | Vigorous effervescence, Mg dissolves, colourless solution |
| Zn + H2SO4 -> ZnSO4 + H2 | Steady effervescence, Zn dissolves |
| Fe + 2HCl -> FeCl2 + H2 | Slow effervescence, pale green solution |
| Mg + H2SO4 -> MgSO4 + H2 | Vigorous effervescence |
Metals below hydrogen (Cu, Ag, Au) do not react with dilute acids.
Test for hydrogen: burning splint gives a squeaky pop.
Pattern 2: Acid + Metal Oxide -> Salt + Water
| Equation | Observations |
|---|---|
| CuO + 2HCl -> CuCl2 + H2O | Black solid dissolves, blue solution forms |
| CuO + H2SO4 -> CuSO4 + H2O | Black solid dissolves, blue solution forms |
| MgO + 2HCl -> MgCl2 + H2O | White solid dissolves, colourless solution |
| ZnO + 2HCl -> ZnCl2 + H2O | White solid dissolves |
| Fe2O3 + 6HCl -> 2FeCl3 + 3H2O | Red-brown solid dissolves, yellow-brown solution |
| Na2O + 2HCl -> 2NaCl + H2O | Vigorous reaction |
These are neutralisation reactions. Metal oxides act as bases.
Pattern 3: Acid + Metal Hydroxide -> Salt + Water
| Equation | Observations |
|---|---|
| NaOH + HCl -> NaCl + H2O | No visible change (both colourless solutions) |
| NaOH + HNO3 -> NaNO3 + H2O | No visible change |
| 2NaOH + H2SO4 -> Na2SO4 + 2H2O | No visible change |
| Ca(OH)2 + 2HCl -> CaCl2 + 2H2O | White solid dissolves |
| Cu(OH)2 + H2SO4 -> CuSO4 + H2O | Blue solid dissolves, blue solution forms |
Ionic equation for all soluble alkali + acid: H+(aq) + OH-(aq) -> H2O(l)
These reactions are the basis of titration.
Pattern 4: Acid + Metal Carbonate -> Salt + Water + CO2
| Equation | Observations |
|---|---|
| CaCO3 + 2HCl -> CaCl2 + H2O + CO2 | Effervescence, solid dissolves, gas turns limewater milky |
| Na2CO3 + 2HCl -> 2NaCl + H2O + CO2 | Effervescence |
| Na2CO3 + H2SO4 -> Na2SO4 + H2O + CO2 | Effervescence |
| MgCO3 + 2HCl -> MgCl2 + H2O + CO2 | Effervescence, white solid dissolves |
| CuCO3 + 2HCl -> CuCl2 + H2O + CO2 | Green solid dissolves, blue solution, effervescence |
| ZnCO3 + H2SO4 -> ZnSO4 + H2O + CO2 | White solid dissolves, effervescence |
Test for CO2: turns limewater milky/cloudy.
Pattern 5: Acid + Metal Hydrogen Carbonate -> Salt + Water + CO2
NaHCO3 + HCl -> NaCl + H2O + CO2
Same products as carbonate reactions. Used in baking and antacids.
Ammonia as a base
NH3 + HCl -> NH4Cl (white smoke of ammonium chloride)
NH3 + HNO3 -> NH4NO3 (ammonium nitrate, fertiliser)
2NH3 + H2SO4 -> (NH4)2SO4 (ammonium sulfate, fertiliser)
Summary table of products
| Reactants | Products |
|---|---|
| Acid + metal | Salt + H2 |
| Acid + base (metal oxide) | Salt + H2O |
| Acid + alkali (metal hydroxide) | Salt + H2O |
| Acid + carbonate | Salt + H2O + CO2 |
Write the equation for the reaction between iron(III) oxide and dilute sulfuric acid. Name the salt formed. [3 marks]
- Fe2O3 + 3H2SO4 -> Fe2(SO4)3 + 3H2O [2]
- Iron(III) sulfate [1]
A student reacts excess copper(II) carbonate with dilute hydrochloric acid to make copper(II) chloride. Describe what the student would observe. [3 marks]
- Effervescence / bubbles of gas (CO2) [1]
- The green solid (CuCO3) dissolves [1]
- A blue solution forms (CuCl2 solution) [1]
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